Cocrystallization of ammonium perchlorate and stabilization of solid propellants

ABSTRACT

A method of improving the thermal stability of double-base propellants containing ammonium perchlorate (AP) by cocrystallization of AP with resorcinol before formation of the propellant grain. AP is dissolved in a solution of liquid ammonia; resorcinol is added to the solution. After evaporation and drying the resulting cocrystals are ground and, in the conventional manner, incorporated into a propellant matrix.

United States Patent [191 Lindsay COCRYSTALLIZATION OF AMMONIUMPERCHLORATE AND STABILIZATION OF SOLID PROPELLANTS [75] Inventor: EdwardK. Lindsay, Cumberland,

[73] Assignee: The United States of America as represented by theSecretary of the Navy, Washington, DC.

[22] Filed: Mar. 5, 1973 [21] Appl. No.: 338,127

[52] US. Cl 149/20, 149/42, 149/76, 149/98, 423/386 [51] Int. Cl C06b11/00 [58] Field of Search 149/20, 76, 42, 98; 423/386 [56] ReferencesCited UNITED STATES PATENTS 3.172.793 3/1965 Markowitz 149/76X Mar. 19,1974 Rice 149/76 Morrow 149/76 X Primary ExaminerStephen J. Lechert, Jr.Attorney, Agent, or FirmP. Schneider; R. S. Sciascia 5 7] ABSTRACT 13Claims, No Drawings COCRYSTALLIZATION OF AMMONIUM PERCHLORATE ANDSTABILIZATION OF SOLID PROPELLANTS BACKGROUND OF THE INVENTION Thisinvention relates generally to a method of stabilizing the deteriorationof solid propellants and more specifically to a method ofcocrystallizing AP and resorcinol to improve the stability ofdouble-base propellants employing AP.

Solid propellants typically contain at least two of the followingingredients: an oxidizer, typically a nideate or perchlorate; a fuel,such as an organic resin or plastic; and a compound combining both fueland oxidizer qualities, such as nitrocellulose or nitroglycerine. Thosepropellants which include nitrocellulose and/or nitroglycerine, whichare capable of combustion in the absence of all other materials, arecalled double-base propellants.

One of the great advantages of solid propellants over liquid propellantsis the longer storage capability of the former. However, many solidpropellants do deteriorate over periods of time. Some experience alow-order chemical reaction during storage, and in various double-basepropellants the decomposition is selfcatalyzing. This decomposition canhave extreme effects on the energy potential of the grain, andpotentially disastrous effects on grain structure.

In the case of double-base propellants containing AP, a reaction betweenthe nitrate esters and AP leads to the formation of gases in thepropellant grain. These gases create voids or pockets in the grain whichcan have an adverse effect on the burning rate. Moreover, duringprolonged storage periods, the formation of gas may produce cracks inthe grain which may ultimately cause total failure of a missile.Generally, stabilizers employed to inhibit the decomposition of thenitrate esters have been added as discrete particles to the propellantmatrix while it was in a workable plastic state. The resultant particledistribution and stabilizer effect were therefore dependent uponmechanical mixing efficiency.

SUMMARY OF THE INVENTION The present invention improves the ability of astabilizer, resorcinol, to inhibit the reaction between AP and thenitrate esters in a double-base solid propellant grain by cocrystalizingthe stabilizer with the AP before incorporation of both into thepropellant matrix. The homeomorphism of the crystals and the intimacy ofthe admixture improve efficiency of stabilization due to the closeproximity of AP and the stabilizer. Cocrystallization will also inhibitsublimation of the resorcinol.

OBJECTS OF THE INVENTION An object of the present invention is toinhibit the reaction between the nitrate esters in a double basepropellant and AP incorporated into the propellant matrix.

Another object is to cocrystallize AP and resorcinol.

A further object of the invention is to inhibit the sublimation ofresorcinol.

Other objects, advantages, and novel features of the invention willbecome apparent from the following detailed description of a preferredembodiment of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT The cocrystallization of AP andresorcinol is best accomplished by employing a liquid ammonia bath.Pressurized ammonia gas can be liquified in a cold-trap submerged in asolid carbon dioxide-acetone mixture. To produce an immediate solutionAP was added to the liquid ammonia to achieve substantially a 1.5 ml/g(Nl-I /AP) volume-to-weight ratio. Resorcinol was then added to thesolution. By weight the resorcinol is l to 10 percent of the AP andresorcinol added to the ammonia, although 3 percent is preferred.

The solution is allowed to evaporate at room temperature until theresulting cocrystals are clamp. The crystals are then dryed at l0O-l50Ffor one-half to one hour. Finally the cocrystals were placed in asubatmospheric chamber at 25 millimeters of mercury at room temperaturefor 16-72 hours. After these drying steps the cocrystals are ground andused to prepare a double base solid propellant grain in the conventionalmanner.

In order that one skilled in the art may practice the present invention,the following table sets forth an example of ingredients which arenecessary to formulate a solid propellant grain.

Parts by weight Ammonium perchlorate-resorcinol 2 .40

Mixing and casting of the above constituents may be carried out inconventional manners applicable to the processing of double basepropellants. It should be noted that the method of stabilizationdescribed is applicable to any double base propellant including AP inits formulation.

Obviously many modifications and variations of the present invention arepossible in light of the above teachings. It is therefore to beunderstood that, within the scope of the appended claims, the inventionmay be practiced otherwise than as specifically described.

What is claimed is:

l. The process of stabilizing the decomposition of nitrate esters in adouble-base propellant containing ammonium perchlorate comprisingcocrystallizing the ammonium perchlorate with resorcinol beforeincorporation into the propellant matrix.

2. The process of claim 1 wherein the cocrystallization is accomplishedby dissolving ammonium perchlorate and resorcinol in a liquid ammoniasolution; allowing the liquid ammonia to evaporate, and drying thecocrystals.

3. An oxidizer for use in a double base solid propellant grain, saidoxidizer comprising, cocrystals of ammonium perchlorate and resorcinol.

4. A method of producing an oxidizer for use in a double-base solidpropellant grain comprising the steps of:

combining ammonium perchlorate and resorcinol in liquid ammonia;

allowing the liquid ammonia to evaporate; and

drying the cocrystals of ammonium perchlorate and resorcinol.

5. The process of claim 2 wherein the ammonium perchlorate is added tothe liquid ammonia to achieve substantially a 1.5 ml/g (NI-MAP)volume-to-weight ratio.

6. The process of claim 5 wherein the resorcinol by weight is l topercent of the ammonium perchlorate and resorcinol added to the liquidammonia.

7. The process of claim 6 wherein the resorcinol by weight is 3 percentof the ammonium perchlorate and resorcinol added to the liquid ammonia.

8. The method of claim 4 wherein the resorcinol by weight is l to 10percent of the ammonium perchlorate and resorcinol combined in theliquid ammonia.

9. The method of claim 8 wherein the resorcinol by weight is 3 percentof the ammonium perchlorate and resorcinol combined in the liquidammonia.

10. The method of claim 8 wherein enough ammonium perchlorate (AP) isadded to the liquid ammonia (NI-l to produce substantially a 1.5 ml/g(NH /AP) volume-to-weight ratio.

ll 1. A double base solid propellant comprising a compound from thegroup consisting of nitrocellulose or nitroglycerine combined withcocrystals of ammonium perchlorate and resorcinol.

12. In combination with a double base propellant an oxidizer comprising:

cocrystals of ammonium perchlorate and resorcinol.

13. A method of producing a double base propellant which comprises:

cocrystallizing ammonium perchlorate with resorcinol to producecocrystals of ammonium perchlorate and resorcinol; and

incorporating the cocrystals into a double base solid propellant.

2. The process of claim 1 wherein the cocrystallization is accomplishedby dissolving ammonium perchlorate and resorcinol in a liquid ammoniasolution; allowing the liquid ammonia to evaporate, and drying thecocrystals.
 3. An oxidizer for use in a double base solid propellantgrain, said oxidizer comprising, cocrystals of ammonium perchlorate andresorcinol.
 4. A method of producing an oxidizer for use in adouble-base solid propellant grain comprising the steps of: combiningammonium perchlorate and resorcinol in liquid ammonia; allowing theliquid ammonia to evaporate; and drying the cocrystals of ammoniumperchlorate and resorcinol.
 5. The process of claim 2 wherein theammonium perchlorate is added to the liquid ammonia to achievesubstantially a 1.5 ml/g (NH3/AP) volume-to-weight ratio.
 6. The processof claim 5 wherein the resorcinol by weight is 1 to 10 percent of theammonium perchlorate and resorcinol added to the liquid ammonia.
 7. Theprocess of claim 6 wherein the resorcinol by weight is 3 percent of theammonium perchlorate and resorcinol added to the liquid ammonia.
 8. Themethod of claim 4 wherein the resorcinol by weight is 1 to 10 percent ofthe ammonium perchlorate and resorcinol combined in the liquid ammonia.9. The method of claim 8 wherein the resorcinol by weight is 3 percentof the ammonium perchlorate and resorcinol combined in the liquidammonia.
 10. The method of claim 8 wherein enough ammonium perchlorate(AP) is added to the liquid ammonia (NH3) to produce substantially a 1.5ml/g (NH3/AP) volume-to-weight ratio.
 11. A double base solid propellantcomprising a compound from the group consisting of nitrocellulose ornitroglycerine combined with cocrystals of ammonium perchlorate andresorcinol.
 12. In combination with a double base propellant an oxidizercomprising: cocrystals of ammonium perchlorate and resorcinol.
 13. Amethod of producing a double base propellant which comprises:cocrystallizing ammonium perchlorate with resorcinol to producecocrystals of ammonium perchlorate and resorcinol; and incorporating thecocrystals into a double base solid propellant.